Polyurethane products, such as foams, resins, and the like, have traditionally been colored by pigments, polymeric colorants, and dyes. Generally, these colorations are performed in situ during foam, resin, etc., formation. For instance, polymeric colorants (i.e., polyoxyalkylenated colorants), such as those described in U.S. Pat. No. 4,284,279 to Cross et al., have been introduced within polyol compositions during slabstock foam production. The "colored" polyol then reacts with an isocyanate composition, in the presence of a catalyst possibly, to form the desired colored foam. Pigments have also been added in the past, most notably in solid, paste, or powder form, to a polyol stream to form the same type of colored foam products. Such foamed products require the presence of a catalyst or catalysts to effectuate the desired reaction between the polyol and isocyanate components. The most prevalent catalysts, due to cost in producing, using, and disposing, are tertiary amine-based compounds. To reduce emissions of residual amine catalysts, the industry has turned to using hydroxyl-terminated type amine catalysts, most notably DMEA and DABCO TL catalysts (a blend of triethylene diamine and 2-[[2-dimethylamino) ethyl]methylamino]ethanol) and Texacot ZF10 (N,N,N'-trimethl-N'-hydroxycthyl-bis (aminoethyl)ether). These catalysts unfortunately present the ability to exaggerate certain problems within the resultant foams, most notably color loss and/or degradations. Apparently, such catalysts react readily with TPM-based chromophores within the polyurethane. The high temperatures associated with polyurethane foam production permits attack of the positively charged TPM polymeric colorant. With a strong positive charge on the base carbon of such a TPM chromophore, the hydroxyls present within the catalyst are drawn to the colorant and appear to react in some fashion to weaken the necessary strong color-producing positive charge. Such deleterious weakening of the TPM positive charge thus apparently causes a severe reduction in color within the foam media. Apparently, such high temperature (i.e., above about 165-185.degree. C.) discolorations and degradations more readily occur between about 15 and 30 minutes after foam generation (after gelation and blowing of the foam-producing composition) has taken place. Without the presence of environmentally unfriendly and thus avoided CFC auxiliary blowing agents, the entire process becomes more excessively heated due to the absence of effective heat dissipation compounds. The high temperatures generated in such a manner thus increase the rate of attack by the hydroxyl of the catalyst on the TPM constituents. As a result, discrete areas within the middle of the final article are discolored as compared with the remaining portions of the article.
One specific, extremely troublesome, problem exists in the utilization of polymeric triphenylmethane colorants within polyurethane foam articles. Such colorants, which comprise highly desirable polyoxyethylene chains, polyoxypropylene chains, or both, provide extremely effective colorations to target polyurethane media. Being polymeric in nature, these colorants actually tend to react to and within the urethane monomers during polymerization. As a result, the color is integrated within the foam and provides excellent uniformity and depth throughout the entire article. However, certain polymerization blowing catalysts, which happen to be the desired catalysts throughout the industry, tend to attack the nitrogen linking groups (present between the TPM backbone and the polymeric chains), thereby degrading the colorants themselves and preventing effective colorations of the target foam article. This phenomenon is most likely caused by the high reactivity of the free amine or hydroxyl groups of the catalysts and their ability to attack the unprotected nitrogens (with free electrons) present on the TPM polymeric colorant.
Attempts at alleviating these particular problems have included the addition of relatively expensive, potentially environmentally unfriendly, and potentially toxic antioxidants, such as 2,6-di-t-butyl-4-methylphenol (BHT), octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propanoate (Irganox.RTM. 1076, from Ciba Geigy), and octyl-3(3,5-di-t-butyl-4-hydroxyphenyl)propanoate (Irganox.RTM. 1135), within the curing process. This has proven ineffective, with little or no improvement in discoloration. Since there is a 15 to 30 minute window of opportunity to control high temperature exposures, some foam producers have practiced forced air cooling of the foam-producing composition in the past to reduce potential discoloration problems. Although such forced air cooling is not required in such an instance, there is a more pronounced color discoloration exhibited upon utilization of consistently high, more inexpensive curing, etc., higher temperatures. Furthermore, since polymeric TPM colorants are the most favorable coloring agents for producing blue and green hue foams, the ability to inexpensively provide readily available TPM colorations within polyurehtane foams is highly necessary. Alternative methods, either simpler and less inexpensive in nature, have not been forthcoming within the industry. As a result, any marked improvements in such a manner are of utmost importance within the polyurethane foam production industry. To date, again, there have been no significant or helpful improvements nor advancements disclosed within the pertinent prior art.